The present invention relates generally to devices for detecting fuel leaks in liquid fuel dispensing systems. More particularly, the present invention relates to a leak detection device having a valve that is inserted in the fuel conduit and which prevents the full flow of fuel upon the occurrence of a leak in the conduit, thereby alerting the operator that a leak exists in the system.
Fuel dispensing stations generally include a large amount of underground piping that is required to produce the fuel supply lines that extend from the underground fuel storage tank to the remote dispensing units. Since the supply lines are disposed underground, any leaks in the lines cannot ordinarily be detected by visual inspection. Consequently, there is the possibility that a leak in an underground line may go unnoticed over a period of time, resulting in the accumulation of flammable fuel in and around the area, thus creating a potentially hazardous condition.
In order to prevent this dangerous condition, leak detectors have been utilized for sensing leakage from underground piping. Typically, such detectors are positioned adjacent the underground fuel storage tanks and monitor the downstream pressure of the liquid fuel in the supply lines between the storage tank and the individual dispensing units. The detectors include a valve that is connected to the supply line. When the submerged pump is actuated, a controlled rate of flow of fuel is initially metered through the detector valve into the supply line. This rate of flow is the maximum rate of leakage of fluid permitted from the underground piping. If a leak is present downstream that equals or exceeds this rate of flow, liquid escapes from the supply line at least the same rate that it enters. In this case, the valve assumes a closed position to restrict the rate of flow greatly below the full rate of flow upon opening of the dispenser nozzle, thereby indicating to the operator that a leak is present in one of the underground supply lines. If no leaks are present, pressure builds up rapidly in the system and causes the detector valve to fully open to allow the fuel to flow at its full rate when the nozzle is opened.
The detection of leaks by pressure sensing detectors is complicated by the fact that fuel is only intermittently pumped through the supply lines. When the pump is started, and the nozzle at the remote dispenser is closed, the pressure in the line will build up to substantially full discharge pressure. When the nozzle is opened, the pressure will drop. While the pump is inactive, the pressure in the line may also vary due to thermal expansion and contraction of the fuel in the line due to changes in temperature. For example, fuel that is pumped from a warm storage tank to cold supply piping can contract significantly, thus decreasing the pressure sufficiently to close the detector valve thereby giving a false indication of a leak and frustrating the operator attempting to dispense the fuel into the gas tank of a vehicle. It is thus necessary to initially pressurize the piping to eliminate the effects of intermittent pump use and thermal contraction. Once pressurized to a predetermined pressure, leak detection may take place.
In the past, metering pins have been used for the dual functions of controlling initial quick pressurization of the system and metering the leak detection rate. The system is initially pressurized by the flow of fuel through a channel between the metering pin and a conduit connecting the fuel inlet and outlet of the detection device. While the system is being initially pressurized, the channel is large enough to allow fuel to flow therethrough at several gallons per minute to provide initial quick pressurization of the downstream conduit. Once the system is sufficiently pressurized, the channel is positioned directly adjacent the metering pin to limit the flow rate through the channel to only several gallons per hour so that leak detection can take place. Due to the bifunctional nature of the metering pins, problems have been encountered in the manufacture, calibration, and operation of the pins.
In addition to problems experienced with metering pins, leak detection devices have experienced problems with the detector valve inadvertently closing during the dispensing of fuel into the motor vehicle. As several nozzles within the fuel dispensing system are simultaneously opened, the pressure in the conduit can drop significantly to as low as about 12 psi, whereas normal operating pressure is about 25 psi. If the submerged pump cannot maintain a sufficient pressure within the conduit while several nozzles are open, there is a possibility that the detector valve will close thereby restricting flow to all of the nozzles and frustrating the operators. It is desired to provide a leak detection device that overcomes these problems.